Recent years, in various electronic devices, their operating frequencies have increased and their packages (especially, their heights) have been downsized. According to such an increase in operating frequency and a reduction in package size, there is also a need for piezoelectric resonator devices (crystal resonators, for example) to be adaptable to the increase in operating frequency and the reduction in package size.
In this kind of piezoelectric resonator, a housing is constituted by a rectangular-shaped package. The package is constituted by: a first sealing member and a second sealing member both made of glass or crystal; and a crystal resonator plate made of crystal. On both main surfaces of the crystal resonator plate, respective excitation electrodes are formed. The first sealing member and the second sealing member are laminated and bonded via the crystal resonator plate. Thus, the excitation electrodes of the crystal resonator plate that is disposed in the package (in the internal space) are hermetically sealed (for example, see Patent Document 1). Hereinafter, such a laminated structure of the piezoelectric resonator is referred to as a sandwich structure.
Meanwhile, Patent Document 2 discloses a crystal oscillator constituted by a semiconductor oscillation circuit element and a crystal resonator that are sealed in one package. In the crystal oscillator, patterns are formed on one surface of the crystal resonator so as to fit a semiconductor oscillation circuit element on one pattern. Also, a bonding pad of the semiconductor oscillation circuit element is electrically connected to the patterns of the crystal resonator.